Brush holder for electric motors



July 13, 1954 c, GERBER 2,683,829

BRUSH HOLDER FOR ELECTRIC MOTORS Filed Jan. 19, 1950 2 Sheets-Sheet l INVEN TOR. Dale 6. Genb er BY ATTOHNE Y.

July 13, 1954 D. c. GERBER BRUSH HOLDER FOR ELECTRIC MOTORS 2Sheets-Sheet 2 Filed Jan. 19, 1950 Patented July 13, 1954 BRUSH HOLDEREOE, ELECTRIC MOTORS Dale G. Gerber, North Canton, Ohio, assignor to TheHoover Company, North Canton, Ohio, a corporation of Ohio ApplicationJanuary 19, 1950, Serial No. 139,463

9 Claims. (01. 310246) This invention relates to electric motors andmore particularly to a cartridge type commutator brush holder therefor.

It is usual practice to provide a longitudinally coiled compressionspring for holding commutator brushes against the commutator. Suchconstructions require that the upper end of the cartridge casing beclosed to form an abutment for the upper end of the spring which must beremoved and replaced each time the brushes are replaced.

In addition, the use of coiled compression springs have a tendency topermit the brush to move sidewise in the cartridge casing and thusproduce brush chatter and a consequent rapid wearing of the brush. It isessential that the pressure between the brush and commutator does not gobelow a minimum. As a result compression springs are designed to givethe necessary minimum pressure when the brush is at its minimum lengthand needs replacement. Thus, when the brush is new the pressure betweenthe brush and commutator is greater than is necessary which results infurther excessive wear of the brush.

According to one feature of the present invention, a tension spring isprovided which does not require the upper end of the cartridge casing tobe closed. Specifically, a flat spring is prestressed so as to naturallywind into a free tight Numerous attempts have been made to prevent brushchatter by holding the entire length of the brush against the trailingedge of the cartridge casing. According to the present invention thatresult can be readily accomplished by merely positioning thecircumference of the free coil against a wedge shaped end of the brush.

According to another object of this invention the hat spring isprestressed in such a manner that it takes a cross sectional camber asit unwinds from the tight volute and the camber is used to press thebrush tightly against the brush holder and thus prevent the brush fromchattering and the resulting excessive wearing away of the brush.

According to another feature of this invention the spring is prestressedin such a manner that as the diameter of the tight volute increases asthe brush wears away to permit more of the spring to wind itself ontothe volute the force tending to rewind the spring onto the coil willremain constant.

Other objects and advantages of this invention will become apparent asthe description proceeds when taken in connection with the accompanyingdrawings in which:

Figure 1 is a plan view of a commutator with a pair of cartridge brushholders associated therewith showing how this invention is applied;

Figure 2 is a view of the invention of Fig. l

volute. lhe one end of the spring is then attaken at right angles toFig. 1; tachecl to the inside of the cartridge casing at its Figure 3 isa view similar to Fig. 2 showing how commutator end and the free coilpositioned over the invention is applied to prevent brush chatter; theouter end of the brush so that the natural Figure 4 is a view of theinvention of Fig. 3 tendency for the spring to rewind itself onto thetaken at right angles to Fig. 3; and coil presses the brush against thecommutator. Figure 5 is a cross-sectional view of a modified Anotherdisadvantage in the use of compresform of the invention. sion springs isthat the pressure applied to the Referring to Figs. 1 and 2, thecommutator is brush decreases as the brush wears away. The representedby the reference numeral ID, the ideal situation is to apply constantpressure to cartridge brush casing by H, the carbon brushes the brushesat all times and complicated linkage 40 by 52, and the pigtailconnections by 13. mechanisms have been suggested for that pur- Flatelongated narrow springs [4 are prepose. According to the presentinvention, such stressed along their length so as to naturallyascomplicated linkage mechanisms are unnecessume a free, tight or solidvolute coil l5 of a disary. As long as the unwound portion of the ameterapproximately the width of the brushes spring is held. in a straightposition, the forces 45 E2. The ends of the springs M are secured totending to rewind it onto the coil have a negligithe interior of thecartridge casing H at their ble effect. the force applied to the brushcommutator ends by rivets It so as to lie between is only that appliedby the free portion of the the brushes i2 and the interior of thecartridge spring between the coil and the end of the brush casing l l.which is substantially constant, 50 The free coils 25 are positionedwithin the cartridge casing H with their edges extending through a slotin the casing and pressing against the outer ends of the brushes l2.

The straight portions of the springs lie between the brushes l2 and thewalls of easing ii and therefore there is no tendency for that portionof the spring to exert a force tending to wind itself onto the coils 55.Thus, the only force pressing upon the brush ends is the force exertedby that portion or" bhE spring between the brush end and the peripheryof the coil 55. It can thus be seen that the inward force exerted on theends of the brushes is substantially constant regardless of the lengthof the brushes.

if the spring is stressed uniformly along its length the inner loop ofthe coil will assume a circle on its natural radius. As more loops arewound about the inner loop, the radius of the coil will increase andpart of the pro-stressed forces will be locked out of action by thetendency to compress the inner loops. Ihus, the coil diameter increasesas the brush is shortened from wear and the force pressing inwardly onthe brushes will decrease slightly as the diameter of the coilincreases. To offset that tendency the spring may be prestressed so asto tend to form a free are or decreasing radius starting from the freeend and extending to the end which is attached to the commutator end ofthe cartridge casing. In other words, the spring is prestressed from endto end in such manner tin t the attached end of the spring will tend toas sume an arc of smaller radius than the radius of the arc its free endtends to assume.

The prestressing of the spring is such that it tends to assume anoutwardly bowed camber as it unwinds from the volute. That will causethe spring to hold the brushes in the cartridge casings against sidewardmovement and thus prevent chatter and the consequent excessive Wear onthe brushes.

The modification of Figs. 3 and l is especially designed to preventchatter of the brushes applying a force tending to hold the entirelength of the brush against the cartridge casing on the trailing side.In this modification axes of the coils 55 are rotated 96 from theposition of Figs. 1 and 2 so that they are parallel to the axis of thecommutator and the slots ll are on the trailing side of the cartridgecasing. The tops of the brushes !2 are wedge shaped and slope downwardlytoward the leading side thereof. Thus, the pressure exerted by the coil55 will hold the outer ends of the brushes l2 against the trailing sideof the cartridge casing and the rotation of the commutator will holdtheir inner ends against it.

That will prevent the brushes from moving sideward in the cartridgecasing to prevent chatter of the brushes and the consequent excessivewear.

Referring to Fig. 5 the brush holder 26 has a channel 2? to receive thespring i5. The channel 26 does not extend the entire width of the holder29 so that shoulders 22 are formed. shoulders 22 form close fittingguides for tl e brush 12 while the channel 21 is of such depth toreceive springs having the maximum camber. in manufacturing springs itis difdcult to make them all with the same camber and according to thismodification the tolerances of the springs need not be held so closelyas in the other modifications.

It is to be noted that in this modification the camber of the springdoes not hold the brush against the side of the holder. In order to ventbrush chatter some expedient such shown in Figs 3 and l may be resortedto.

From the foregoing, it can be seen that this invention provides anarrangement in which the commutator brushes are given a substantiallyconstant pressure regardless of the length thereof and are preventedfrom chattering. in each modification it only necessary to pull thecoils outwardly of the cartridge casing in order to replace brushes.

While I have shown but two modifications of my invention, it is to beunderstood that these modifications are to be taken as illustr and notin a limiting sense. I do not wish to be limited to the particularstructure shown and described, but to include all equivalent variationsthereof except as limited by the scope or" the claims.

I claim:

1. A. commutator brush holder comprising, an elongated brush casing, anda elongated spring in said casing and or a w n to fit edge- Wise in saidcasing having a straight portion at one end secured to the commutatorend of and within said casing and its other coi. into prethat springextends into said casing heter thereof and a brush positioned ther y thetendency of the straight portion of spring to rewind itself is lockedout of action.

3. A commutator brush holder according to claim 2 in which said springis prestressed 1g its length in such manner that the free end forms asolid coil whereby the entire length of said spring tends to rewinditself about coil.

4. A commutator brush holder according to claim 3 in which said springis prcstressed in such manner as to form an outward camber as it isunwound from said coil whereby camber Will press against the brush insaid casing to hold it from chattering yet permit it to move freelythrough said casing.

5. A cartridge type commutator brush comprising, an elongated brushholder in the form of a casing, a carbon brush in said and a flatelongated spring inside said casing ha ng a fiat portion at one endsecured to the interior of said casing at the commutator end thereof andextending outwardly along the side of s d brush and having its free endcoiled a seirewinding volute resting against the outer end of saidbrush.

6. A commutator brush according to claim 5 in which said spring isprestressed along its entire length so as to tend to wind itself tightlyabout said volute.

7. A commutator brush according to claim 6 in which the outer end ofsaid brush wedgeshaped having its long edge at the trailing le of saidcasing whereby said spr ng tends to hold the outer end of said brushagainst the trailing side of said casing.

8. A commutator brush according to claim 5 in which the prestressing ofsaid spring varies along its length in such manner hat the commutatorend of said spring tends to form an arc of smaller radius than that ofits free end.

9. A commutator brush according to claim 5 in which said holder isprovided with a channel 5 6 for receiving said, spring and said springis pre- Number Name Date stressed so as to form an outwardly bowed1,964,280 Witchger June 26, 193}; camber as it is unwound from saidvolute. 1,977,546 Fornelius Oct. 16, 1934 2,273,644 Hope Feb. 17, 1942References Cited in the file of this patent 5 2,280,735 Weissinger Apr.21, 1942 UNITED STATES PATENTS 2,647,743 (300k u 1953 Number Name DateFOREIGN PATENTS 2,288 Smith DEC. 26, 1871 Number Country Date 65 Van D ple F 2 1890 10 603,159 Germany Sept. 25, 1934 gofig l l J I- g 658,776Germany Apr. 11, 1938 un e u y 697,432 Bassett Apr. 15, 1992 OTHERREFERENCES 728,273 Mix May 19, 1903 Publication Product Engineering,July 1.949, 1,488,575 Wagner Apr. 1, 1924 F pages 136 to 140. 1,495,203Robel'g May 27, 1924

